.\" $OpenBSD: ohash_init.3,v 1.2 2014/05/13 14:01:41 jmc Exp $ .\" Copyright (c) 1999 Marc Espie .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .\" $FreeBSD: head/lib/libopenbsd/ohash_init.3 269250 2014-07-29 19:46:13Z joel $ .\" .Dd May 12, 2014 .Dt OHASH_INIT 3 .Os .Sh NAME .Nm ohash_init , .Nm ohash_delete , .Nm ohash_lookup_interval , .Nm ohash_lookup_memory , .Nm ohash_find , .Nm ohash_remove , .Nm ohash_insert , .Nm ohash_first , .Nm ohash_next , .Nm ohash_entries .Nd light-weight open hashing .Sh SYNOPSIS .In stdint.h .In stddef.h .In ohash.h .Ft void .Fn ohash_init "struct ohash *h" "unsigned int size" "struct ohash_info *info" .Ft void .Fn ohash_delete "struct ohash *h" .Ft "unsigned int" .Fn ohash_lookup_interval "struct ohash *h" "const char *start" "const char *end" "uint32_t hv" .Ft "unsigned int" .Fn ohash_lookup_memory "struct ohash *h" "const char *k" "size_t s" "uint32_t hv" .Ft void * .Fn ohash_find "struct ohash *h" "unsigned int i" .Ft void * .Fn ohash_remove "struct ohash *h" "unsigned int i" .Ft void * .Fn ohash_insert "struct ohash *h" "unsigned int i" "void *p" .Ft void * .Fn ohash_first "struct ohash *h" "unsigned int *i" .Ft void * .Fn ohash_next "struct ohash *h" "unsigned int *i" .Ft "unsigned int" .Fn ohash_entries "struct ohash *h" .Sh DESCRIPTION These functions have been designed as a fast, extensible alternative to the usual hash table functions. They provide storage and retrieval of records indexed by keys, where a key is a contiguous sequence of bytes at a fixed position in each record. Keys can either be NUL-terminated strings or fixed-size memory areas. All functions take a pointer to an ohash structure as the .Fa h function argument. Storage for this structure should be provided by user code. .Pp .Fn ohash_init initializes the table to store roughly 2 to the power .Fa size elements. .Fa info is a pointer to a .Fa struct ohash_info . .Bd -literal -offset indent struct ohash_info { ptrdiff_t key_offset; void *data; /* user data */ void *(*calloc)(size_t, size_t, void *); void (*free)(void *, void *); void *(*alloc)(size_t, void *); }; .Ed .Pp The .Va offset field holds the position of the key in each record; the .Va calloc and .Va free fields are pointers to .Xr calloc 3 and .Xr free 3 Ns -like functions, used for managing the table internal storage; the .Va alloc field is only used by the utility function .Xr ohash_create_entry 3 . .Pp Each of these functions are called similarly to their standard counterpart, but with an extra .Ft void * parameter corresponding to the content of the field .Fa data , which can be used to communicate specific information to the functions. .Pp .Fn ohash_init stores a copy of those fields internally, so .Fa info can be reclaimed after initialization. .Pp .Fn ohash_delete frees storage internal to .Fa h . Elements themselves should be freed by the user first, using for instance .Fn ohash_first and .Fn ohash_next . .Pp .Fn ohash_lookup_interval and .Fn ohash_lookup_memory are the basic look-up element functions. The hashing function result is provided by the user as .Fa hv . These return a .Qq slot in the ohash table .Fa h , to be used with .Fn ohash_find , .Fn ohash_insert , or .Fn ohash_remove . This slot is only valid up to the next call to .Fn ohash_insert or .Fn ohash_remove . .Pp .Fn ohash_lookup_interval handles string-like keys. .Fn ohash_lookup_interval assumes the key is the interval between .Fa start and .Fa end , exclusive, though the actual elements stored in the table should only contain NUL-terminated keys. .Pp .Fn ohash_lookup_memory assumes the key is the memory area starting at .Fa k of size .Fa s . All bytes are significant in key comparison. .Pp .Fn ohash_find retrieves an element from a slot .Fa i returned by the .Fn ohash_lookup* functions. It returns .Dv NULL if the slot is empty. .Pp .Fn ohash_insert inserts a new element .Fa p at slot .Fa i . Slot .Fa i must be empty and element .Fa p must have a key corresponding to the .Fn ohash_lookup* call. .Pp .Fn ohash_remove removes the element at slot .Fa i . It returns the removed element, for user code to dispose of, or .Dv NULL if the slot was empty. .Pp .Fn ohash_first and .Fn ohash_next can be used to access all elements in an ohash table, like this: .Bd -literal -offset indent for (n = ohash_first(h, &i); n != NULL; n = ohash_next(h, &i)) do_something_with(n); .Ed .Pp .Fa i points to an auxiliary unsigned integer used to record the current position in the ohash table. Those functions are safe to use even while entries are added to/removed from the table, but in such a case they don't guarantee that new entries will be returned. As a special case, they can safely be used to free elements in the table. .Pp .Fn ohash_entries returns the number of elements in the hash table. .Sh STORAGE HANDLING Only .Fn ohash_init , .Fn ohash_insert , .Fn ohash_remove and .Fn ohash_delete may call the user-supplied memory functions: .Bd -literal -offset indent p = (*info->calloc)(n, sizeof_record, info->data); /* copy data from old to p */ (*info->free)(old, info->data); .Ed .Pp It is the responsibility of the user memory allocation code to verify that those calls did not fail. .Pp If memory allocation fails, .Fn ohash_init returns a useless hash table. .Fn ohash_insert and .Fn ohash_remove still perform the requested operation, but the returned table should be considered read-only. It can still be accessed by .Fn ohash_lookup* , .Fn ohash_find , .Fn ohash_first and .Fn ohash_next to dump relevant information to disk before aborting. .Sh THREAD SAFETY The open hashing functions are not thread-safe by design. In particular, in a threaded environment, there is no guarantee that a .Qq slot will not move between a .Fn ohash_lookup* and a .Fn ohash_find , .Fn ohash_insert or .Fn ohash_remove call. .Pp Multi-threaded applications should explicitly protect ohash table access. .Sh SEE ALSO .Xr hcreate 3 , .Xr ohash_interval 3 .Rs .%A Donald E. Knuth .%B The Art of Computer Programming .%V Vol. 3 .%P pp 506-550 .%D 1973 .Re .Sh STANDARDS Those functions are completely non-standard and should be avoided in portable programs. .Sh HISTORY Those functions were designed and written for .Ox .Xr make 1 by Marc Espie in 1999.